Subject: Protocol Action: An RTP Payload Format for Generic Forward Error Correction to Proposed Standard

From: The IESG <[email-masked]>
Date: Fri, 15 Oct 1999 08:33:47 -0400

The IESG has approved the Internet-Draft 'An RTP Payload Format for
Generic Forward Error Correction' <draft-ietf-avt-fec-08.txt> as a
Proposed Standard.  This document is the product of the Audio/Video
Transport Working Group.  The IESG contact persons are Scott Bradner
and Vern Paxson.

Technical Summary
 
The document provides a means of providing FEC for an RTP flow by XOR'ing
together data packets to generate a separate FEC stream.  The FEC format is
generic in the sense that it works with arbitrary algorithms for deciding
which data packets to combine and how many FEC packets to generate.  There
are two ways in which the FEC data may be transported: as a separate RTP
flow, or by piggy-backing onto the original flow using the RFC2198 "redundant
audio" payload format.

Working Group Summary

The FEC process was not controversial in AVT, and the draft includes
appropriate warnings about misuse.  The draft was held up in the working
group for some time because it proved difficult to define SDP parameters to
describe transport of FEC as a separate flow.  A clean solution would require
grouping the FEC flow with the original media flow, but SDP doesn't support
grouping. The solution adopted in the draft is to include an SDP connection
specification as a codec parameter, indicating where the FEC information for
a flow is to be found.  This is ugly, but the only workable solution the
WG found.

Protocol Quality

The document was reviewed for the IESG by Vern Paxson.